The present invention relates to a supervisory control method and equipment for smart grids, which comprise diesel generators, gas turbine generators and distributed power sources using natural energy, to realize a stable operation by integrated and autonomous control of the distributed power sources in case of a load change or an accident.
The smart grid utilizes the latest digital information and communications technology to realize a power supply network that carries out interconnected management and operation efficiently by unifying information on various centralized power sources (such as hydraulic, thermal and nuclear power generations), power distribution networks and distributed power sources (such as solar power generation, wind-power generation, and diesel generator) with consumers (offices, factories, and ordinary homes). The smart grid network can monitor and control the flow of electricity and can also flow electricity and information bidirectionally between the power generating plants and the consumers.
In order to do that, it is considered that it is also necessary to perform independent operation for stabilization of voltage and frequency by the smart grid itself without relying on the commercial power system for compensation of the load change in the future, and it is also considered that the stand-alone operation of the distributed power sources is significant to enhance the independence of the distributed power sources from the commercial power system.
The smart grids dispersedly arranged close to the above consumer regions are attracting attention as smart grids serving as a complement to the existing large-scale power source, and it is necessary to interconnect them to the existing commercial power system in order to fully exert the role.
When the smart grid connected to the commercial power system falls in an islanding operation including other general consumer loads due to a power line or distribution line accident, it is required to parallel off the other general consumer loads from the distribution system as soon as possible from viewpoints of power supply reliability and maintenance. Here, the islanding operation means a state that power is supplied continuously by the smart grid only even if the power supply from the large-scale power source stops.
Therefore, various islanding operation detection devices have been developed and put into practical use for detection of the islanding operation of the smart grid. The islanding operation detection devices are largely classified into a passive type and an active type.
The islanding operation detection device of the passive type keeps supervising a measurable state quantity such as voltage and frequency variations, variations in high-frequency distortion and a phase shift at an interconnection of the distributed power sources, and detects the islanding operation through the use of a fact that the above values are variable largely in comparison with the ordinary interconnected power system state when the operation falls in the islanding operation. For example, JP-A 2002-281673 occasionally has a change in output frequency of the generator when the islanding operation occurs and then detects the islanding operation when the frequency change rate becomes a threshold value or more.
The islanding operation detection device according to the active type keeps applying disturbance from the smart grid side to the power system and monitors system phenomena of voltage and frequency when the islanding power system occurs and detects the islanding operation early. Japanese Patent No. 3367371 introduces interharmonics which are not in the commercial power system and detects system impedance at the time of abnormalities to detect the islanding operation state. But, the active type has the power capacitor constantly connected to the power system, and if power system noise such as a flicker load is large, it causes unnecessary operation, so that it is necessary to conduct an investigation such as prior measurement.